Manufacturers of disk drives have relatively recently moved from using thin-film inductive ("TFI") heads to magneto-resistive ("MR") heads to perform the disk drive's read functions. One of the main reasons for the switch is due to the greater sensitivity of MR heads over TFI heads. As a result, areal densities have dramatically increased.
Due to their sensitivity, however, MR heads sometimes pickup spurious signals emitted by power transformers, motors and the like. In an effort to reduce or eliminate the pickup of the aforementioned spurious signals, disk drive manufactures have placed shields around the MR heads. Such shields, however, have caused additional problems.
Specifically, the shields have been found to be susceptible to variations in their magnetic states. These variations can be magnetically coupled to the MR head which can cause unwanted shield-related side readings. For the most part, the data regions of the magnetic disk have not caused problematic variations in the magnetic state of the shield because the information placed on the disk is written in the data regions in a relatively random fashion. However, the servo regions of the disk have caused problematic magnetic variations in the shields and, hence, problematic shield-related side readings, due to the fact that servoburst patterns are written in a radially coherent manner.
The above-described shield-related side readings can cause, among other things, a decrease in (1) the linear range of the MR head when reading off-track servo information; and, (2) the off-track signal-to-noise ratio. Furthermore, in extreme cases, the shield-related side readings can cause the disk drive to completely malfunction.
Accordingly, there is a need to minimize and/or eliminate the magnetic variations in the shields which can cause shield-related side readings. The present invention is designed to overcome the aforementioned problems and meet the aforementioned, and other, needs.